1. Field of the Disclosure
The present disclosure relates to an electromagnetic brake unit and, more particularly, to an electromagnetic brake unit that can maintain a good operation feeling.
2. Description of the Related Art
Recently, instruments provided with input devices, mounted on vehicles and the like, and operable to fit various modes for in-vehicle temperature setting, car audio volume adjustment, car navigation and the like are available. Some of the input devices have an electromagnetic brake unit so that an operation range of an operator can be limited in response to input details of the various modes. It is required for the input devices that have such an electromagnetic brake unit to be capable of maintaining a sufficient braking force exceeding an operating force of the operator when a brake is applied by the electromagnetic brake unit and, moreover, to be capable of operating smoothly without a feeling of being caught at a time of non-braking. The applicant has filed an electromagnetic brake unit using a rotary input device according to Japanese Patent Application No. 2012-38806 as such electromagnetic brake unit. Also known as a similar technique is an electromagnetic brake unit used in a rotary input device according to Japanese Unexamined Patent Application Publication No. 2010-62075.
The electromagnetic brake unit used in a rotary input device 900 according to Japanese Patent Application No. 2012-38806 will be described referring to FIG. 12. FIG. 12 is a cross-sectional view showing a configuration of the rotary input device 900 according to Japanese Patent Application No. 2012-38806.
In the rotary input device 900 according to Japanese Patent Application No. 2012-38806, a friction plate 908 that is disposed to be connected to an operation unit 902, which is rotation-operated is magnetically adsorbed by an electromagnetic brake 909 so that a braking force is applied and the rotating operation is limited. The friction plate 908 and the electromagnetic brake 909 are always in contact with each other. However, at a time of non-braking without the magnetic adsorption, the friction plate 908 is pivotable in conjunction with an operation that is added to the operation unit 902 and a good operation feeling is provided. Also, at a time of braking with the magnetic adsorption, the electromagnetic brake 909 magnetically adsorbs the friction plate 908 with an electromagnetic force, the friction plate 908 and the electromagnetic brake 909 are in closer contact with each other, and frictional resistance increases so that the braking force is exerted and the rotating operation is limited. In order to maintain the good operation feeling at a time of non-braking and generate the braking force with reliability at a time of braking, a metallic material is used in a friction surface and a surface of the electromagnetic brake 909 that is in contact with the friction surface and a smooth and hard thin film layer is formed on the contact surface by a physical vapor deposition method (PVD method).
It is assumed that the rotary input device 900 according to Japanese Patent Application No. 2012-38806 is forcibly operated by an operator against the braking even at a time of braking. The forcible operation against the braking results in wear debris on the smooth and hard thin film layer formed by the PVD method, which is caused by wear due to sliding and micro-vibration. The hard wear debris acts as a grindstone to accelerate sliding wear, and a scratch is likely on the contact surface between the friction plate 908 and the electromagnetic brake 909. It is concerned that the scratch may exacerbate the operation feeling during the rotating operation by generating the feeling of being caught.